Accumulator for hydraulic systems



June 9, 1964 P. WlLDl ETAL ACCUMULATOR FOR HYDRAULIC SYSTEMS Filed June 17, 1960 FIG.2

INVENTORS PAUL WILDI GEORGE R. KOCH BY ATTORNEY United States Patent Ofifice 3,136,340 Patented June 9, 1964 The present invention relates to apparatus for actuating hydraulic systems, commonly called accumulators, in which a gas under high pressure is contained in a tank and is separated from hydraulic fluid (also under pressure) by either an elastic bladder or by a piston. Accumulators are useful for various purposes as, for example, in the hydraulically actuated circuit breakers of Patent No. 2,662,134 issued December 8, 1953, to D. M. Urnphrey. The gas is under pressure and the pressure in the accumulator increases when a hydraulic pump forces hydraulic fluid into the accumulator. The pressure in the gas and in the hydraulic system is decreased when it releases some of its stored energy, which occurs upon opening of a valve which produces hydraulic operation. So long as the hydraulic-system valve remains closed, the hydraulic fluid should remain under sustained high pressure. The diaphragm or the piston functions essentially as a separator or divider to keep the gas and the hydraulic fluid apart.

The gas pressure encountered in such hydraulic system is often quite high, 2,800 pounds per square inch in an example. The accumulator is initially charged with gas under pressure, using a valve which, conventionally, is externally accessible. The valve provides a filling port, but additionally it is used in replenishing the supply of pressurized gas which tends to escape gradually over long periods of time. Maintenance of gas volume and pressure is of vital importance to the functioning of the accumulator, despite long idle intervals.

The gas-filling valves of hydraulic accumulators have caused considerable trouble in practice, since the gas tends to leak out through the filling valve. This is true even when a tight cap is used over the filling valve.

A feature of the present invention resides in arranging the filling valve in such manner as to completely eliminate the pressure ditferential that otherwise tends to cause the valve to leak; and a further feature resides in the elimination of the valve seals, as well as all other seals between the gas-filled compartment of the accumulator and the external atmosphere.

In one embodiment of certain aspects of the invention, a gas-filling valve is provided in the movable wall of the illustrative hydraulic accumulator. When the system is pressured and ready for use, high-pressure gas at one side of the movable Wall in the accumulator is bal The filling valvein the movable dividing wall is thuseffective for admitting the gas without however resort to a valve that is exposed to the high-pressure differential between the internal gas chamber of the accumulator and the outside atmosphere.

In a second embodiment of the invention, the barrier between the compressed gas and the hydraulic fluid is partly stationary and partly movable; and the valve is located in the stationary portion of the divider. In this embodiment the broad purposes of the first embodiment are achieved, but certain advantages are peculiar to each embodiment, as will appear.

Hydraulic accumulators areused for instant operation of hydraulic equipment such as circuit breakers, as noted above, and in such applications it is of critical importance that the pressure and volume of gas shall be sustained and shall not leak oif even during prolonged idle periods of time. Accordingly, a primary object of the invention is to provide a novel accumulator having a gasfilling valve which is substantially proof against the normal leakage of gas that heretofore has characterized such accumulators. Regarded otherwise, the present invention resides in various novel features contributing to stable, reliable storage of gas under high pressure in an accumulator, in a manner to reduce the possibility of leakage of gas to an absolute minimum.

The nature of the invention and its various features of novelty will be better appreciated from the following detailed description of an illustrative embodiment of the invention which is shown in the accompanying drawings. In the drawings:

trative accumulator embodying features of the invention, and

FIGURE 2 is a like view of another embodiment of the invention. Referring to FIG. 1, a cylinder 10 is shown having a dome 12 integral therewith. Cylinder 10 and dome 12 are made of heavy-walled steel, formed as a drawn cup so as to be seamless and free of all joints between the gas compartment and the exterior through which pressurized gas might escape. The inside wall 10a is formed as a precise cylindrical surface with a micro finish. A header 14 is joined to the end of cylinder 10 opposite dome 12, having an O-ring seal 16 as of synthetic rubber and having a clamping ring 18 for securing header 14 to cylinder 10. Hydraulic line 20 is threaded into an opening 22 in header 14, line 20 extending to the hydraulic system to be actuated and to a pressure-restoring hydraulic pump. Between header 14 and dome 12 there is a floating piston 24 which forms a barrier or wall separating the upper chamber 26 from the lower chamber 28. Pressurized gas, normally nitrogen, fills chamber 26 and a suitable hydraulic fluid such as oil fills the lower chamber 23. The piston with its sealing ring 27 prevents gas from coming into contact with the oil and thus prevents loss of the gas which has some limited tendency to dissolve in the oil.

Aligned with opening 22 there is a valve 30 threaded and gasketed to an opening 32 in piston 24. This valve includes a spring 34 which biases a ball-valve against a valve seat formed in valvebody 38. A cap 40 is threaded over the lower endof the valve body 38. Opening 22 is aligned with cap 40 and valve30 and is of greater diameter than cap 40 so that gas pressure can force piston 24 against header 14 as a stop, and both valve body 38 and cap 40 can be manipulated as required during the gascharging operation.

In normal operation, chamber 26 is filled With a gas such as nitrogen at a high pressure, 2,800 lbs. per square inch in an example. Chambe r 28 is filled with oil, and is at the same pressure under steady-state conditions. When a valve in the system connected to hydraulic line 20 is opened, the gas in chamber 26 expands and forces hydraulic fluid from chamber 28 into hydraulic line 20. Thereafter, hydraulic fluid is pumped back into chamber 28 from a suitable-automatically controlled pump forming part of the hydraulic system.

Under steady state conditions there is no pressure difference between chambers 26 and 28; and because of this FIGURE 1 is a vertical cross-section through an illusv there is no tendency of the pressurized gas to escape either through the unitary cylinder and dome 12 which forms a container or through the piston or movable wall 24. Even when piston 24 moves down suddenly (as occurs when hydraulic fluid is delivered to the hydraulic system) there is only moderate, momentary pressure difference between the chambers 26 and 28. Valve 30 is provided with cap 40, as previously mentioned, and this prevents any flow of hydraulic fluid from chamber 28 into chamber 26 at such times.

When it is necessary to introduce gas under pressure into chamber 26, hydraulic line 20 may be removed, cap 40 may be removed and a gas supply connection may be made to valve body 38 for filling chamber 26. Access to cap 40 and valve 30 is gained via opening 22. After the required gas pressure is established in chamber 26 with piston 24 at the bottom of cylinder 14-, cap 40 is restored as shown and hydraulic line 20 is returned to place in opening 22.

It might be considered that, because filling port 30 is not readily accessible, that this would be a detriment. However, because of the pressure differential across piston 24 is virtually non-existent and because the remainder of the gas-filled part of the container that includescylinder and dome 12 is free of joints exposed to the atmosphere, there is only a remote possibility that pressurized gas once charged into chamber 26 will have to be renewed. The construction described provides great assurance that the pressurized gas will not escape and will be reliably reliable when needed.

In the foregoing embodiment of the invention the movable wall is in the form of a piston which is guided along a cylindrical bore that is formed directly in the inside surface of the container. It is also known however that a false cylindrical wall may be provided within the container for receiving and guiding the piston.

One such arrangement is illustrated in FIG. 2 wherein primed numerals are used to designate corresponding elements found also in FIGURE 1. Thus in FIGURE 2 a drawn seamless cylindrical container 10' has an integral compartment, plugs 62 and 40 may be removed, and a' pressure line may be inserted in place of plug 40' for admitting gas to the space within container 10' above flange 56 and above piston 24'. Valve closes as soon as the delivery of pressurized'gas to the upper'space of chamber 19' is interrupted. Thereafter plugs 49 and 62 are again inserted. When hydraulic fluid pressure is built up in the hydraulic system and transmitted to the accumulator via hydraulic line 2%), piston 24' is. forced upward and the gas pressure increases somewhat.

The embodiment of FIG. 2 differs from that of FIG. 1 as previously noted in that the piston does not move against the inside surface of the heavy-walled container; in thataccess to the filling valve is gained not through the opening provided for the hydraulic line but, instead, is

dome 12 and, at the opposite end, a header 14 is joined to container 10' by clamping ring 18'. A seal 16' is provided between header 14 and container 10. Header 14 has an opening 22' threaded to receive hydraulic line 20' which extends to the rest of the hydraulic system as previously described.

As indicated in the drawing of FIGURE 2, a movable piston 24' forms part of the structure that divides the space within the container 10' into separate chambers for compressed gas and hydraulic fluid, respectively. Piston 24 does not operate against the wall of container 10' (as in the case of FIGURE 1) but instead piston 2d operates along a relatively thin-walled cylinder 50 that is loosely confined axially between a series of ribs 52 inside dome 12 and a series of rods 54 carried by header 14'. Cylinder 50 is capable of limited endwise shift, as may occur during actuating operations, but this is of little consequence. Cylinder 50 has an integral flange 56 that fits closely against the inside wall of chamber 10' and a seal 5% is also provided between the inside wall of chamber 10' and the rim of flange 56. Flange 56 and that part of cylinder 50 below piston 24' form a stationary portion of the barrier between the compressed gas and the hydraulic fluid, and movable piston 24 completes this barrier.

A valve 30' is mounted in flange 56, and a removable plug or cap normally closes off the opening from the oil chamber to the inlet side of valve 30. A shouldered opening 60 is formed in header 14, and a plug 62 is tightly received in this opening, with the usual sealing ring.

With the parts arranged as shown in FIG. 2, the normal operation of the system is the same as has been described in connection with FIG. 1. There is no appreciable pressure difference between the gas chamber and gained through a separate normally sealed opening in header 14'; and in that the valve through which gas is introduced is in a fixed partof the apparatus rather than in the movable barrier between the two spaces provided for pressurized gas and hydraulic fluid, respectively. However, the broad concept is preserved of avoiding a large pressure differential between the confined gas and either the valve or a gasket relative to the outside atmosphere. The only seals between the pressure part of the system and the outside atmosphere in both FIGS. 1 and 2 exist between the high-pressure hydraulic fluid part of the system and the outside atmosphere, and with proper seals the hydraulic fluid is retained. This arrangement consequently reduces to a bare minimum any possible depletion of the pressurized gas in the space provided in the accumulator.

The foregoing description of two illustrative embodiments of the invention represent preferred forms as presently contemplated. Nevertheless it will be apparent that variations in detail and varied application of the invention will occur to those skilled in the art; and consequently the invention shouldbe broadly construed in accordance with its full spirit and scope.

Having thus described my invention, what I claim as new and desire to secure by Letters Patent is:

1.'An accumulator for hydraulic apparatus including an elongate rigid gas-tight container having a fixed volume and an opening in one end thereof, said container being imperforate and seamless at its opposite end, means for removably securing a hydraulic line to said opening, separating means for dividing said container into first and second chambers and including pressure responsive means freely movable between said chambers, said first chamber being defined by the one end of said container and said separating means and said second chamber being defined by the imperforate other end of said container and said separating means, each of the opposite sides of said pressure responsive means being exposed to one of said chambers so that said pressure responsive means will move in a direction tending to equalize the pressure on the opposite sides thereof, passage means extending through said separating means for conducting gas to said second chamber and having an inlet exposed to said first chamber, and shutoff means for said passage means.

2. An accumulator for hydraulic apparatus including a rigid gas-tight container having an opening formed in one portion thereof and the remaining portion being imperforate, means at said opening for connection to said apparatus, separating means for dividing said container into first and second chambers and including pressure responsive means freely movable between said chambers, said first chamber being defined by said one portion of said container and said separating means and said second chamber being defined by the imperforate remaining portion of said container and said separating means, each of the opposite sides of said pressure responsive means being exposed to one of said chambers so that said pressure responsive means will move in a direction tending to equalize the pressure on the opposite sides thereof, passage means extending through said separating means for conducting gas to the other of said chambers and shutoff means normally closing said passage means.

3. The accumulator set forth in claim 2 wherein said shutoff means includes a valve disposed in said passage means and including a pressure responsive spring biased element constructed and arranged to open when the gas pressure at the one chamber side thereof is higher than that at the opposite side thereof.

4. The hydraulic accumulator set forth in claim 2 wherein said separating means comprises a piston.

5. The hydraulic accumulator set forth in claim 2 wherein said separating means includes a stationary por-- tion, said passage being provided through said stationary portion.

6. The hydraulic accumulator set forth in claim 2 wherein said separating means includes a cylinder, a piston disposed in said cylinder and a flange portion extending between said cylinder and the wall of said container, said passage means being provided through said flange portion.

7. An accumulator for hydraulic apparatus including a rigid gas-tight container having an opening in one end thereof and being closed at its opposite end, a freely movable piston disposed in said container for dividing the same into first and second chambers, said first chamber being defined by said one end of said container and said piston and said second chamber being defined by the closed other end of said container and said piston, each of the opposite sides of said piston being exposed to one of said chambers so that said piston will move in a direction tending to equalize the pressure on the opposite sides thereof, a gas-filling passage extending through said piston so that gas may be conducted to said second chamber from said first chamber, and means for closing said gas-filling opening.

8. An accumulator for hydraulic actuating apparatus including a heavy-walled seamless metal cylinder having an imperforate integral dome at one end, a header secured to the end of the cylinder opposite said dome, said header having an opening and a formation at said opening for connection to a pressure line of the hydraulic apparatus, a piston between and exposed to said dome and said header, a passage through said piston opposite said header opening, and a valve in said piston passage, said valve having a spring-biased valve member bearing against a valve seat therein and arranged to be opened by a greater pressure at the header side of the piston than at the dome side, and a closure covering the header end of the valve, said closure being aligned with said header opening and accessible therethrough for removal when gas is to be charged into the accumulator.

9. An accumulator for hydraulic apparatus including an elongated unitary seamless gas-tight container having only one open end, a header covering said open end, separating means within said container for dividing the space within the container into two main chambers for pressurized gas and hydraulic fluid, respectively, said separating means having a passage therethrough for charging the pressurized-gas chamber, shut-off means normally closing said passage, and an access opening in said header opposite said shut-01f means for connecting a pressurized gas supply line to said passage which thus extends through said hydraulic fluid chamber during gas-charging operations, said separating means including a movable barrier for maintaining substantial pressure equality between the two chambers during stand-by conditions and operable to drive hydraulic fluid from said accumulator under pressure when demanded by the hydraulic apparatus.

10. An accumulator for hydraulic apparatus including an elongate rigid gas-tight container having a fixed volume and an opening formed in one end thereof, said container being imperforate at its opposite end, means for removably securing a hydraulic line to said opening, a freely movable piston dividing said container into first and second chambers, said first chamber being defined by the one end' of said container and one side of said piston and said second chambers being defined by the imperforate end of said container and the other side of said piston, valve means extending through said piston for conducting gas to said second chamber and having an inlet end exposed to said first chamber.

References Cited in the file of this patent UNITED STATES PATENTS 2,417,873 Huber Mar. 25, 1947 2,703,108 McCuistion Mar. 1, 1955 2,715,419 Ford Aug. 16, 1955 2,743,741 0rd May 1, 1956 2,748,801 McCuistion June 5, 1956 2,943,642 Westcott July 5, 1960 

1. AN ACCUMULATOR FOR HYDRAULIC APPARATUS INCLUDING AN ELONGATED RIGID GAS-TIGHT CONTAINER HAVING A FIXED VOLUME AND AN OPENING IN ONE END THEREOF, SAID CONTAINER BEING IMPERFORATE AND SEAMLESS AT ITS OPPOSITE END, MEANS FOR REMOVABLY SECURING A HYDRAULIC LINE TO SAID OPENING, SEPARATING MEANS FOR DIVIDING SAID CONTAINER INTO FIRST AND SECOND CHAMBERS AND INCLUDING PRESSURE RESPONSIVE MEANS FREELY MOVABLE BETWEEN SAID CHAMBERS, SAID FIRST CHAMBER BEING DEFINED BY THE ONE END OF SAID CONTAINER AND SAID SEPARATING MEANS AND SAID SECOND CHAMBER BEING DEFINED BY THE IMPERFORATE OTHER END OF SAID CONTAINER AND SAID SEPARATING MEANS, EACH OF THE OPPOSITE SIDES OF SAID PRESSURE RESPONSIVE MEANS BEING EXPOSED TO ONE OF SAID CHAMBERS SO THAT SAID PRESSURE RESPONSIVE MEANS WILL MOVE IN A DIRECTION TENDING TO EQUALIZE THE PRESSURE ON THE OPPOSITE SIDES THEREOF, PASSAGE MEANS EXTENDING THROUGH SAID SEPARATING MEANS FOR CONDUCTING GAS TO SAID SECOND CHAMBER AND HAVING AN INLET EXPOSED TO SAID FIRST CHAMBER, AND SHUTOFF MEANS FOR SAID PASSAGE MEANS. 